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which is supported by two strong arms working on trunnions, and four oblique rods—two on each side. The two arms extend io or 12 inches beyond the trunnions, and each carries a counterpoise half the weight of the telescope. It will be observed that these weights project on the opposite sides of the declination axis, and, when properly adjusted, exactly balance the telescope, so 'that the centre of the upper disc becomes absolutely the centre of gravity of the whole mass, Now at this point an enormous improvement is effected by the simplest possible means, consisting merely of a small plate and two differential screws so arranged as to throw the entire weight of the telescope and upper plate upon the end of the pivot. By this contrivance friction is reduced to a minimum, and movement by hand or by a clock becomes extremely easy.

Spanning the upper disc at right angles to the axial line is a semicircular arch, having the same diameter. Upon this arch the divided declination scale is fixed, and the vernier is attached to the cradle of the telescope. The slow movement in declination is produced by a tangent screw rod, which can be clamped to any part of the above-named arch. That in right ascension is as follows :—Passing through the polar axis is a strong rod on the lower end of which the driving wheel acted upon by the clock may be attached, if such a power is employed. The upper end of the rod is fixed to a disc on the edge of which an endless screw is cut, and working in this is a tangent screw, the end bearings of which are fixed to -the upper main disc. If the rod and disc are clamped together a direct motion is communicated from the clock to the telescope, and any independent movement can be given by revolving the tangent screw. Should it be requisite to move the telescope rapidly through a large space, either the clamp can be released, or the tangent screw thrown out of action without interfering with the driving clock.

The slow movements and clamps in right ascension and declination are worked by handles placed close by the eye-piece, and therefore very accessible. The circles can be read from the eyepiece end of the telescope. The right ascension circle can be connected to the driving clock so that when once set it will show sidereal time as long as the clock is in motion, thus greatly facilitating right ascension readings. The driving clock is made with firm, large wheels, regulated by governors. It can be readily stopped without risk of injury ; the time it will work without being re-wound depends on the length of the drop allowed for the weight, 3 to 4 hours is the usual duration. The entire clock is protected from injury and dust by enclosure between the sides of the stand and a removable glass front. The stand is so constructed that the telescope can be turned throughout the 24 hours when pointing to the pole. The above description, in its entirety, only refers to specification C in the catalogue. A and B are modified.

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Le texte affiché peut comporter un certain nombre d'erreurs. En effet, le mode texte de ce document a été généré de façon automatique par un programme de reconnaissance optique de caractères (OCR). Le taux de reconnaissance estimé pour cette page est de 99,53 %.

La langue de reconnaissance de l'OCR est l'Anglais.

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